The Justice of Reincarnation
The Zohar on the opening of Parshas Mishpatim says that here are the secrets of reincarnation, and the commentators ask what the connection is. The Degel explains that sometimes a beis din obligates a man to pay when he knows the man is innocent. This is not a flaw in Torah law, since the man may have been guilty in a past life and the time has come to make restitution. The Zohar links reincarnation to the laws of judgments so that we recognize the true justice of the Torah.
Source: Degel Machaneh Ephraim, Mishpatim